Take on a tube amp (let's see if i'll manage to)

[vendettav]

Hey guys. so recently i got this idea.. i cant get rid off...

I am really considering to start a tube amp build and see if i can accomplish it. if i can get into the groove of making 5 watt tube amps a lot of people would be interested in here: reason 1 - no tube amps available here for sale reason 2 - importing from abroad costs a bunch reason 3 - no tube amp makers in our region (that is caucasus, i bet some guys from georgia would also get interested)

ok now i know this is not a kid dream and it's gonna be hard but well if you don move your ass nothing's gonna happen at all

so first of all

I have some understanding in electronics. Pedal builds and whatnot. still on my way of learning but that way never ends right?  

so http://pluto.spaceports.com/~fishbake/champ/chmp.gif this schematic is quite interesting
I've done a lot of reading on this topic and i get the whole thing now but some questions I have so far are:

1. what exactly do i need? let's make a full list of the stuff needed and see if it's affordable for me
2. what parts could be scavenged? (for the prototype only) I'm in a post soviet country so they've got a lot of transformers and sh*t here for really cheap. What should I look for in transformers and tubes when looking for some?
3. any help with making a chassis? I'll probably ask someone doing metal stuff to make one for me

guess that's it for now
thanx in advance

[amptramp]

The amplifier design looks quite reasonable.  I don't know if your standard power there is 117 VAC or 220 VAC and 50 Hz or 60 Hz, but if there are differences in the areas you intend to sell them in, you need a transformer that can handle the minimum frequency and all voltages (usually done with two windings on the primary that are connected in series for 220 VAC and parallel for 117 VAC).  And of course, you need a plug that will fit in the wall socket that may be round or flat-blade contacts.  His article:

http://pluto.spaceports.com/~fishbake/champ/chmp.htm

shows some interesting mods you may want to try before you order large quantities of stuff.  Make sure your country and the countries you intend selling in do not need approvals such as UL, CSA, TUV or some other such safety approval in order to sell them.

Following your questions:

1. Make up a parts list from the schematic.  The coupling and tone stack capacitors should be film types rated at 600 or 630 volts.  Then you have to add mechanical parts such as the chassis, tube sockets, terminal strips, knobs, shielded wire (if you are using it), ordinary wire etc. - just look at a normal tube radio and see what items do not show up on a schematic.  Unless otherwise stated, resistors should be 1/2 watt to survive typical amplifier handling abuse and temperature rise.  One technique used to make amplifiers suitable for an abusive handling environment (getting tossed into a van, dropped on the road etc.) is to use a turret board with a larger insulating board under it so it can all be screwed to the chassis.  Traynor used this and could drop their amps out of a second-storey window without mishap.

2. You may be able to get transformers, but are they the right ones?  The power transformer secondary will carry about 60 mA and you can do with less B+ voltage - you will have about 390 volts whereas you can get 5.5 watts out of a 6V6 with 330 volts using cathode bias as shown.  A 250-0-250 VAC secondary will be more than adequate for this.  The filament supply will be 0.75 amps and this circuit does not have a pilot light, so if you need one operating from the heater supply, add that current to it.  The output transformer should be 8500 ohms to 8 ohm single ended.

3. Chassis can be either bought as basic undrilled items or folded up from flat by a local machine shop.  Either way, you will need to do a drawing showing hole sizes and locations.  Precision costs money, so don't ask for any tighter tolerances than you need.

[vendettav]

thanx mate, that's a lot of information there
some stuff is a bit far from my point now (as the more of a business approach to the wohle building/selling) but hope i'll soon get to that point as well

ok now for the tonestack the caps are 600~ volts? that's gonna cost some money, hmm a good idea would be to omit the tone stack then for the prototype build

I was actually reading the article and liked the whole thing. also the mods were quite simple and interesting

so everything is clear except the Scavenging part.
we've got 220v 50Hz here if im not mistaken (about the Hz) so... what do i want? something that takes in 220v and puts out 300V ac and 6.3V ac ? is this all the info needed to explain them what i need? (they usually know the soviet parts but they dont know the modern parts so finding a substitute you need to tell them every single thing so that they know what you want ) and same about the output transformer: 8500 ohm in and 8 ohm out? no voltage ratings right? (sorry i've never really gotten to work with transformers)

another thing. at the power transformer: the 6.3VAC to the heaters. it all goes to the pins 4, 5 and 9 on 12ax7 and 2 and 7 on 6v6?

and hmm can i get soviet subs for the tubes? what shall i look for again?

[amptramp]

When you first turn the amplifier on, the tonestack parts are connected by resistors from plate supply to ground.  This puts full voltage across them since there is no current drain until the tubes begin to conduct.  This voltage drops once the tubes start conducting, but it is always a good idea to be generous on voltage rating - it increases the reliability.

If you have 220 VAC 50 Hz, then this is what you should be scrounging and it should also be what is available.  You need a 250-0-250 VAC secondary at 60 mA and a 6.3 VAC winding at 0.75 amps.  These are minimum values for current rating.  More is always welcome but don't forget, the voltage outputs are at the rated current, so if you get a transformer with 200 mA B+ output and 4 amps filament output, check the voltages with the load you will be using.

Output transformers usually do not have voltage specifications, but most are insulated for their normal application.

You have the correct heater pins.  You should make use of the online tube manual at www.duncanamps.com to get pinouts.

There should be soviet subs for certain tubes since the 12AX7 and the 6V6 are common audiophile devices.  Use the online tube manual to determine whether the ratings (which govern survival in a particular circuit) and the performance parameters (gain, plate resistance etc.) are suitable for your use.  There are other tubes such as horizontal deflection tubes that can be used to make good audio output stages and are plentiful and cheaper than the common audio tubes, but you may have to change the cathode resistor and increase the filament and plate current ratings and reduce the screen voltage - basically, a redesign.  As an option, the capacitor across the 470 ohm cathode resistor for the 6V6 is optional.  Deleting it reduces the stage gain but also extends the low-frequency response.  Whatever you do, do not mount it right beside the cathode resistor - I have seen capacitors get leaky enough to actually reduce the cathode bias at high temperatures, and this does not show up until the amplifier has been on for about 15 minutes and the capacitor gets hot.

[vendettav]

ok thta seems to make sense, hope they'll know what I want in the store...

I also found some subs from russian forums for those tubes hopefully i'll be able to locate them as well

ok now another interesting question, what should i mount the parts on. i mean the electrolytics and the resistors... what board shall it be?

[amptramp]

I wouldn't use a printed circuit board for this kind of project.  The tube sockets, controls and transformers should mount to the chassis and other components should be mounted on a board.

My preference for a board is an epoxy-glass or phenolic turret board which has two rows of terminals that look like they were turned on a lathe.  Second best is a terminal board that has two rows of terminals that are stamped from flat metal with holes in the terminals for attaching component leads.  Either of these should mount on top of a slightly larger epoxy-glass or phenolic board so that the underside of the terminals are prevented from touching the chassis.  This whole assembly is bolted to the chassis along the centreline.  This is the type of construction used by Traynor, who tested his amplifiers by tossing them out of a second-storey window and would only go into production once the amplifier passed this test.  (I live about a mile west of Toronto, where Traynor amplifiers were made and I have rebuilt a Traynor YVM-66 amplifier for a girl who is a friend of my daughter.  The construction is simple but capable of withstanding brutal treatment.)  Equipment designed for touring musicians get abused regularly during transport, so make sure the construction is rugged and reliable.  For example, you might want a spring-loaded tube shield and matching socket hardware to make sure the 9-pin tube does not accidentally fall out and you may want a bear-trap retainer for the octal tube.  The (TUA) COLLAR-9P tube socket collar and (TUA) TS103U03 shield are shown on this page:

http://www.surplussales.com/tubes-sock-acc/TubeShields-1.html

On this page, RET-3 is a bear-trap retainer that is bolted down with the octal socket and is spring-loaded so it grips the tube:

http://www.radiodaze.com/tube-plugs.htm

[vendettav]

hmm wonder if i'll be able to locate all that stuff for tubes... this country is not a tube country at all i mean they don't carry anything modern much...
also for the board// hmm wonder if i'll be able to find one. you think a pref board would work? I think yeah cause like it won't have much weight on it will it?

[boogietone]

... this country is not a tube country at all i mean they don't carry anything modern much...

Sorry, this was just too funny!

Good luck with your build!

[thedefog]

I know you mentioned you have trouble getting parts and whatnot in your country, but have you considered starting off with a kit, like a Weber amp kit? I built a 6a14HP from there, and I think it is better sounding than my 68 Twin Reverb.

https://taweber.powweb.com/store/kits.htm

There is also a lot of information on their forum regarding not just their kits, but all tube amps, especially the champ.

Good luck!

[vendettav]

... this country is not a tube country at all i mean they don't carry anything modern much...

Sorry, this was just too funny!

Good luck with your build!

yeah i see yoru point but no... whati meant by that is that they dont carry anything built past 1960 lol... so anything you find is gonna be older than your mom...

as for the weber kits.. hmm what's the cheapest kit? i can see actually no point in buying something for more than 150 or something (and the shipping is gonna cost a lot) and selling it for like 200 .. that'll be barely 10 or 20 bux of income.. which is no good at all. yeah fine for the starting point but tube amps aren't something people buy everyday

[slacker]

There's some good information here about building valve amps using cheap and salvaged parts.
http://www.ozvalveamps.org/ava100/ava100project.htm
The stuff about voltage multiplier power supplies is particularly useful, because it shows you how to make high voltage supplies without using special transformers. I've built an amp using the info in there and apart from the output transformer and the tag strip to build it on all the parts were from a general electronics supplier.

[boogietone]

You might check on sourcing the transformers locally as they are the most expensive and the heaviest parts

[vendettav]

yeah transformers and the tubes are my general concern...
still havent been to a store but it's a good idea to gather as much of info as possible before going there right?

[amptramp]

yeah transformers and the tubes are my general concern...
still havent been to a store but it's a good idea to gather as much of info as possible before going there right?

Make sure you can get everything you need before you get anything.  I worked as a project manager at one time and the concerns for project management are different from academic concerns.  If you get 99% in an exam, you have done very well.  If you can get 99% of the parts you need for a project, that is the worst case, because you have committed most of your money but you still can't manufacture the product and get paid, so you are in the worst possible financial position.

If you are buying surplus items, make sure you can get the quantity you need.  I use anything that is available for a one-off pedal build.  I would have to use what I can get in quantity if I want to go into production.

[vendettav]

yeah transformers and the tubes are my general concern...
still havent been to a store but it's a good idea to gather as much of info as possible before going there right?

Make sure you can get everything you need before you get anything.  I worked as a project manager at one time and the concerns for project management are different from academic concerns.  If you get 99% in an exam, you have done very well.  If you can get 99% of the parts you need for a project, that is the worst case, because you have committed most of your money but you still can't manufacture the product and get paid, so you are in the worst possible financial position.

If you are buying surplus items, make sure you can get the quantity you need.  I use anything that is available for a one-off pedal build.  I would have to use what I can get in quantity if I want to go into production.

thanx That's actually the lines i was thinking along i mean I prefer to make sure i can find everything before attempting to buy something. especially when it's a tube amp not like a little booster where you can toss the caps and resistors away for later project you know...

thanx that also makes sense. i guess what i want now is to first make the prototype and then see if people are interested and if they'll want to order some.. this way I'll be able to use components from say Banzai Music (shopped from them and they're good, also one of the very few stores that ships to my country)

anyways i feel it's gonna take a lot of thinking and planning before i can even go to scavenge some stores but i better not risk it and hurry it up